The new protocol will be signed Monday, shortly before President Obama opens a summit in Washington on keeping nuclear material out of the hands of terrorists, officials said. More than 40 heads of state are expected at the summit.

The new protocol amends an agreement signed by then-Vice President Al Gore and the Russian leadership in 2000 under which the two countries pledged to get rid of 34 tons of plutonium each. The material came from weapons that had been decommissioned.

The total 68 tons would be enough for 17,000 nuclear bombs, officials said.

The 2000 agreement stalled over Moscow's unhappiness with the process by which the material was to be turned into fuel for civilian power plants. In addition, the world's leading industrialized countries never came up with the $2 billion they had promised Russia to convert the plutonium.

Under the amended Plutonium Management and Disposition Agreement, Russia will dispose of the plutonium in two fast-neutron reactors, said the officials, speaking on the condition of anonymity because the protocol is not yet public. The agreement will include conditions on safeguarding the material, officials said.

Russia will pay most of the costs, but the U.S. government will chip in $400 million, officials said. One-quarter of that is requested in the 2011 budget.

Kenneth N. Luongo, a senior nuclear nonproliferation official in the Clinton administration, said the agreement was originally intended as a powerful sign of shrinking stockpiles. "It was supposed to be a declaration of our intentions to move beyond the Cold War," he said.

But experts also worry about the security of plutonium because only a small amount, roughly the size of a grapefruit, would be needed to build a nuclear bomb.

Negotiations on the protocol began more than two years ago, under the Bush administration. The document will be signed in the midst of a rush of activities related to Obama's ambitious nuclear agenda. The president this week signed an arms-reduction treaty with Russia and issued a new nuclear weapons policy.

It still may take eight years for the two countries to start disposing of the plutonium because of the complex technical procedures involved. They expect to finish around 2030, officials said.